x^-xy-2y^=0怎么化简成(x-2y)(x+y)=0

x^-xy-2y^=0怎么化简成(x-2y)(x+y)=0
x^-xy-2y^=0怎么化简成(x-2y)(x+y)=0

x^-xy-2y^=0怎么化简成(x-2y)(x+y)=0
∵x²-xy-2y²
=x²-xy-y²-y²
=(x²-y²)-(xy+y²)
=(x+y)(x-y)-y(x+y)
=(x+y)(x-y-y)
=(x+y)(x-2y)
∴x²-xy-2y²=0可化为(x-2y)(x+y)=0

十字相乘法啊，没学吗？
1\ / -2
1/ \ +1

x^2-xy-2y^2=0
用十字相乘
x -2y
x y
所以x^2-xy-2y^2=(x+y)(x-2y)=0

x²-xy-2y²=x²+xy-xy-xy-2y²=x²+xy-2xy-2y²=x(x+y)-2y(x+y)=(x-2y)(x+y)
啊 真辛苦。。。。
年轻人 你代数要认真学了。。。